Blackrock has been trimming their position for close to a month now. They are the top institution holding AAPL. They've been selling "as many shares as they can" at $120 nonstop. Reason for selling is nothing more than a gamble on earnings and also because it represents a huge portion of their portfolio. They are wishing to reinvest in other markets. As soon as earnings are out they'll stop selling, especially if apple gaps out.